Cell migration is an essential component of normal function of hematopoietic cells in development and immune surveillance, and of endothelial cells in wound healing and angiogenesis. Migration is also involved in disease states such as chronic inflammation, autoimmune disease, cancer and pathological angiogenesis. The goal of this proposal is too understand the signaling mechanisms that initiate, guide and coordinate cell migration. We will study a monocytic and an endothelial cell line to allow comparison of two cell types that play important roles in hematopoietic and vascular biology and that may serve as models for understanding distinct mechanisms of migration employed by circulating vs. constitutively adhesive cell types. Understanding migration requires elucidating the spatial and temporal regulation of signaling, adhesive and cytoskeletal events within a cell. These events include the adhesion of migrating cells to extracellular matrix (ECM) proteins, a process that is mediated by integrins, whose affinity state is controlled by intracellular signaling pathways such as Ras/ERK and phosphoinositide 3-kinase. The Rho family GTPases, Rac and Cdc42, initiative key intracellular pathways that govern cytoskeletal organization and polarity in moving cells. In addition, mechanical forces exerted on the ECM through integrins serve to move the cell forward and to coordinate the pathways that govern cytoskeletal organization. Therefore, our approach here will be to 1) elucidate the mechanisms that govern localized activation of integrins; 2) characterize the local activation of Rac and Cdc42 in specific regions of the cell; 3) identify the pathways that regulate localized application of contractile forces to the ECM; and 4) identify mechanisms by which mechanical forces feed back to regulate localized activation of Rac and Cdc42. Taken together, these experiments may provide novel insights and potential molecular targets to inhibit or enhance these experiments may provide novel insights and potential molecular targets to inhibit or enhance cell migration pharmacologically in pathological or desirable circumstances, respectively.